1. Field of the Invention
This invention is generally related to a welding apparatus, especially the type that utilizes a consumable welding wire which is fed from a supply reel, through a wire feeder assembly and subsequently to a welding gun. More particularly, this invention provides an apparatus and method for selectively changing welding wire prior to the welding wire entering a wire feeder assembly for subsequent feeding to a welding gun.
2. Description of the Prior Art
Welding is broadly accomplished by bringing a gun tip of a welding gun into close proximity with a work piece. The power supply and wire feeder assembly are energized by depressing a trigger on the welding gun, which also causes welding wire to move through a flexible conduit leading to the gun tip of the welding gun and be propelled forwardly therefrom. When the welding wire contacts a grounded work piece, electrical current passes through the welding wire to the work piece, causing the welding wire to be heated and melt. An electrical arc is established which continues to melt the welding wire and causes transfer of melted welding wire to the work piece where it fuses and cools. The electrical energy supplied to the welding system is greater than that required to melt the welding wire. Most of the remaining energy in the form of heat is transferred to the surface of the work piece, melting the surface metal on the work piece for improving the bonding of melted welding wire to the work piece. As the welding gun is moved across the work piece, melted welding wire is continuously transferred to the work piece as long as the trigger is depressed and as long as welding wire is available. If the welding operation requires a shielding gas, a gas valve is actuated when the trigger is depressed.
In the course of normal welding, the supply of welding wire will eventually be depleted. When this occurs, the welder or operator will shut down the welding system. In the case of a robot or other automatic welding process, the operator will initiate a safety lockout procedure and enter the welding area. After entering the welding area, the operator will obtain a pair of pliers and grasp the end of the welding wire protruding from the gun tip of the welding gun and pull out any welding wire remaining in the flexible conduit extending to the gun tip. The operator will then remove an empty welding-wire spool from a dereeler and replace it with a new spool of welding wire. The loose end of the welding wire is subsequently threaded through guides and conduits extending to a wire feeder assembly that includes spring loaded pinch rollers which are manually released to allow the welding wire to be threaded through associated feeder guides and into the flexible conduit. The spring loaded pinch rollers are then reapplied. The operator subsequently energizes welding-wire feed by means of a switch (or gun trigger) and the welding wire is propelled through the flexible conduit until it exits the gun tip of the welding gun. Typically, an excess of welding wire comes out of the gun tip. The excess is manually trimmed with side cutter pliers, or in the case of a robot welding process where there is often an automatic stationary cutter available, the robot directs excess welding wire into the automatic stationary cutter where the excess is removed. The welding system is now ready to continue welding.
Many welding operations weld more than one type of metal. Different types of metals require different welding wire compositions. For instance, an operator may be welding mild steel work pieces using a suitable steel wire. If the work pieces change to stainless steel, the operator has to remove the existing spool of steel welding wire and install a spool of suitable stainless steel welding wire. A typical procedure to change welding wire requires a number of steps. Initially, the operator trims the welding wire sticking out of the gun tip. This trimming operation is for removing a ball of metal on the end of the welding wire which is a result of surface tension pulling molten metal up the welding wire when the welding process stops. If a robot system is being employed, the operator directs the robot to use the automatic stationary cutter to remove the ball of metal from the end of the welding wire. The operator then manually releases the spring loaded pinch rollers on the wire feeder. The wire storage spool is subsequently manually rotated in a reverse direction to pull welding wire from the gun tip through the flexible conduit and through the wire feeder. The loose end of the welding wire is then anchored on the spool and the spool is removed. A spool of stainless steel welding wire is subsequently installed. The loose end of the welding wire is then threaded through the wire feeder until it reaches the entrance of the flexible conduit. The spring loaded pinch rollers are reapplied and the wire feeder is energized to feed the welding wire to the gun tip where excess welding wire is trimmed. The operator may now commence welding with stainless steel welding wire.
Therefore, welding wire has to be changed in a wire welding process for two primary reasons. The first primary reason is that the supply of welding wire has been depleted and additional welding wire is required to continue the welding process. The second primary reason for changing welding wire is that the composition of the welding wire has to be changed to accommodate a new welding application. For example, the welding process may be welding mild steel with steel welding wire. If the work pieces change to stainless steel, then an appropriate stainless steel welding wire is required for the new application. Both of the foregoing reasons for changing welding wire produces downtime in the welding operation which should be reduced. The prior art, as evidenced by the following prior art which was discovered in a patentability investigation, does not offer a more optimum solution for reducing downtime in a welding operation when a welding wire has to be changed.
U.S. Pat. No. 3,694,620 to Gleason discloses an electric arc welding system using two welding wires fed through a single torch, with means (e.g. a motor) for driving either welding wire in either direction. U.S. Pat. No. 4,645,894 to Bonga discloses an electrode wire changer and threading mechanism which is capable of handling two or more different types of electrode wires which are for cutting through a work piece.
Japanese Patent No. 36,066 teaches a welding wire supply device. This patent discloses the use of air cylinders as a means for pressing a wire against a drive roller in order that the wire may enter a guide cable for eventual passage through a wire detector. Japanese Patent No. 100,870 discloses a welding device which is similar to what is disclosed in U.S. Pat. No. 3,694,620 to Gleason. Japanese Patent No. 168,967 appears to also teach a system that is comparable not only to U.S. Pat. No. 3,694,620 to Gleason, but also comparable to U.S. Pat. No. 4,645,894 to Bonga. Japanese Patent No. 233,067 teaches that a driving means may be used to move a mechanism to select one of a plurality of feeding wires for feeding to a torch.
The foregoing prior art does not offer a more expedient apparatus and method for changing a welding wire with reduced downtime in a welding process. Therefore, what is needed and what has been invented is an apparatus for selectively changing consumable welding wires such that downtime is reduced in a welding process. What is also needed and what has been invented is a method for selecting any one of a plurality of consumable welding wires without incurring any substantial downtime in a welding operation.